CSA demands and threatening letters

I have been trying to solve my problem with the CSA for many years to no avail.

My two ex wifes initially went to the CSA when we broke up but after the dust settled and things became amicable they informed the CSA they did not require the services and wanted no monies collecting on their behalf, I pay for holidays, school uniforms, phone contracts and pay money weekly my ex partners are more than happy, but these parasites won’t leave me alone they tell me I have a 12k debt and they are going to take my car etc, what i cant make them understand is no one wants this money but them! I am literally running scared that the next thing is they will find out where i work and take money from me that way.

They are even calling my ex partner and asking for my whereabouts. i have tried talking to them but i have totally given up. they are now sending me letters that are discussions from march 2010! I would greatly appreciate the help of anyone out there. A distressed loving father!